Better control of baghouses and cartridge-type dust collectors can pay dividends in energy savings, longer filter life and effort spent in tracking environmental compliance. That’s the message from Richard Kapcha, a control specialist with MikroPul (Charlotte, N.C.), which manufactures a wide range of dust collection equipment. “Until the early 1990s we were supplying baghouses with cleaning cycles based on fixed time intervals,” Kapcha says. “Many of these timer systems are still in use. Changing to a cleaning routine based on differential pressure can save a large plant tens of thousands of dollars a year.”
By cleaning filters only when they need it, differential-pressure control systems lengthen filter life as well as saving compressed air, Kapcha adds. MikroPul’s recently launched PulsePro EC control unit (photo) uses reliable solid-state pressure sensors to check the cleaning status of one or more dust collectors, and relay the results to a control room. As well as managing the cleaning cycle, the PulsePro EC monitors compressed-air use, allowing it to detect energy-wasting valve diaphragm failures. And, it also measures and records particulate levels in the exhaust air. As reporting requirements become more stringent, Kapcha says, the ability to log this information automatically saves time and paperwork headaches; it also detects bag failures.
A new particulate emission monitor and baghouse leak detector from FilterSense (Beverly, Mass.; photo, p. 25) incorporates automatic self-checking to improve performance and eliminate manual calibration, which would otherwise be required by the EPA’s MACT and CAM regulations governing fabric-filter dust collectors. Smart diagnostics and a proven induction sensing technique increase reliability compared to sensors based on measurements of opacity or triboelectricity, FilterSense says, making the unit ideal for difficult applications such as coal, steel, cement, carbon black, lead smelters and pharmaceutical spray dryers. The company also supplies “pass/fail” particulate detectors and non-clogging pressure transmitters.
To clean filter bags and cartridges effectively using the minimum of compressed air, Asco Joucomatic Numatics (Ölbronn-Dürrn, Germany) has launched a 1.5-in. version of its successful type 353/800 Power Pulse solenoid valve. Specifically designed for dust collectors, the valves feature a patented piston design that enables significantly faster opening and closing, quieter operation, and lower air consumption with no compromise in cleaning performance, the company claims. Options include a rapid mounting system, and a version with a remote pilot valve for applications where space is at a premium. The standard design can operate at temperatures up to 85°C, with a 150°C model available, and version are available for hazardous atmospheres.
Changing regulations affecting dust filters and baghouses go beyond environmental protection, notes Sal Campos, marketing services manager with Farr Air Pollution Control (Jonesboro, Ark.). Recent updates to standards published by the National Fire Protection Assn. (NFPA; Quincy, Mass.; www.nfpa.org) have increased the range of applications for which dust filters and baghouses require explosion venting, he says. As a result, Farr’s flagship Gold Series cartridge dust collector is now available with a built-in explosion vent. The new multi-ribbed “X-vent”, which is made of stainless steel and can be retrofitted to existing dust collectors, meets NFPA and ATEX standards. Units in the modular Gold Series range in size from single cartridges up to 150,000-CFM (ft3/min) housings containing 140 cartridges, Campos says.
Finding a finer filter
Instrumentation and explosion protection notwithstanding, key to the performance of any type of cartridge or fabric filter is the filter medium chosen. Farr’s Gold Series dust collectors, for instance, are fitted with HemiPleat filter cartridges, which are resistant to moisture, highly efficient (99.99% for particles of 0.5 µm and larger), and have a wide, uniform pleat spacing for maximum dust capacity and easy cleaning. The latest HemiPleat HE (High Efficiency) cartridges (photo, p. 25) go one better, with an efficiency of 99.999% for particles down to 0.5 µm, and a MERV (Minimum Efficiency Reporting Value) of 15. The company claims that these typically provide twice the life of standard cartridges, at half the pressure drop.
According to some manufacturers, nanofibers provide better filtration performance and cleanability than the standard fibers of cellulose acetate, glass and thermoplastics traditionally used for cartridges and filter bags. United Air Specialists (UAS; Cincinnati, Ohio) recently launched a range of cartridge filters based on nanofibers just 70–150 nm in diameter (photo, p. 25); the company says this is around half the diameter of the nanofibers in competing products.
UAS marketing manager Lisa Wilhelmus says the MERV 15-rated nanofiber filters typically have twice the life of standard cellulose and 80/20 cellulose/polyester cartridges, and use up to 60% less compressed air for cleaning. “The filters are durable, because the nanofibers have very good adhesion to the substrate material,” Wilhelmus says, “and the distribution of nanofibers is very even, so there are no large ‘holes’ that can let particles through.”
The Donaldson Torit division of filter systems manufacturer Donaldson Co. (Minneapolis, Minn.) has been making nanofiber filters for 25 years, and in January this year launched an improved version of its Ultra-Web product. With a layer of nanofibers atop a spunbond polyester substrate, Ultra-Web SB is a tough filter medium that is ideal for fibrous or abrasive dusts, explains marketing manager Julie Rumsey. “Getting perfect adhesion to the backing material was a technical challenge,” she says, but the resulting resin-free construction ensures good resistance to heat, moisture and chemical attack, while wide pleats aid cleanability. Ultra-Web SB is available in both cartridges (photo, above) and filter bags. Donaldson Torit also offers cartridge filters with Ultra-Web nanofibers on cellulose and synthetic substrates, as well as PTFE membrane filters with spunbond substrate.
For installations using bag filters instead of cartridges, Midwesco Filter Resources, Inc. (Winchester, Va.) says its Seal-Tite II pleated elements (photo) are easier to install than any other bottom-load filter bag on the market today. The proprietary sealing and clamp system saves installation time, creates a virtually leak-proof seal, and makes incorrect installation practically impossible, the company claims. The washable filter bags are long-lasting, thanks in part to the elimination of inlet abrasion problems, and offer dust removal efficiencies up to 99.99%.
Another design of pleated bag is MikroPul’s Mikro-Pleat, said to be the only snap-in bag with an integral venturi. The company’s Grapoid tool, which is powered by a cordless drill, allows snap-in pleated and felt bags to be removed in around 10 sec. each, with little effort. For even easier bag changing, MikroPul Pop-Top 2 bags replace standard snap-in bags and seal with simple foot pressure.
Choose the right housing
Important as the filter bag or cartridge is, a well-designed housing is also essential to create an effective installation. AAF International (Louisville, Ky.) has launched the ArrestAll AR Series self-contained, shaker-type dust collector for intermittent and light-duty applications. The compact unit has a top-mounted fan with easy access for servicing, 16 filter pockets as standard, an automatic shaker mechanism with an adjustable timer for cleaning, and a silencer; an integral final HEPA filter is optional. A side door makes filter changing easy, and a tough powder coating protects the metal parts.
Pneumatic conveying specialist Cyclonaire Corp. (York, Neb.) has launched a range of environmental protection products under the name “445 Technology”, in reference to the target of limiting atmospheric carbon dioxide to 445 ppm suggested by the U.N. Intergovernmental Panel on Climate Change. The range includes the C&C automated dust reclaim system (photo, p. 27), which captures dust from silo filling operations. Other products collect dust from the unloading and filling of sacks and intermediate bulk containers (IBCs), and from pneumatic conveyors.
Micro Air (Wichita, Kan.) makes cartridge-type filters units with capacities up to 100,000 CFM, explains national sales manager Jim Orr. The company’s recently-launched RP-1 Twister (photo, p. 25) is a compact unit rated at 1,000 CFM that combines an upstream cyclone with a cartridge filter. The unit measures just 18.5-in. dia. and 64 in. high. Cleaning is via Micro Air’s exclusive Roto-Pulse cartridge cleaning system, which is said to clean 100% of the cartridge area. Applications include capturing dust from grinding operations and bag filling.
Among the range of dust collection devices available from Scientific Dust Collectors (Alsip, Ill.) are two types of heavy-duty horizontal cartridge units with reverse-pulse cleaning: the SL and the SL-HR. The SL is a compact housing for up to 24 cartridges, and handles flows of 1,800–15,600 CFM. The more advanced SL-HR (High Ratio) is suitable for larger flows, operating at flowrates of up to 1,000 CFM per cartridge. This is around twice the specific flowrate of the SL, and is made possible through a patented cleaning system and innovative cabinet design, the firm says.
For locations where compressed air for filter cleaning is not available, the RAC series of dust collectors from Sly, Inc., (Cleveland, Ohio) may be useful. Instead of an external compressed air supply, this design uses an internal blower powered by an explosion-proof motor. A rotating cleaning arm carrying a series of nozzles directs high-velocity air jets onto the filter bags to remove dust. Sly RAC dust collectors are available for air flowrates of 4,500–70,000 CFM. The company also manufactures other wet, dry and combination wet/dry dust collection systems.